[Python-ideas] PEP 479: Change StopIteration handling inside generators

[Devin Jeanpierre]

On Mon, Nov 17, 2014 at 9:40 AM, Guido van Rossum <guido at python.org> wrote:
> I don't want to contemplate a new __next__ protocol. The existing protocol
> was carefully designed and tuned to have minimal memory overhead (even to
> the point where the exception instance returned may be reused). Wapping each
> result would just result in an extra allocation + deallocation per
> iteration, unless you can play games with reference counts or do something
> else to complicate the semantics). Introducing __nextx__ would require
> thousands of libraries implementing this to incur churn as they feel the
> pressure to switch to the new protocol, and the compatibility issue would be
> felt everywhere.

This sounds totally reasonable to me.

> The problem we're trying to fix is unique to generators (thereby also
> implicating generator expressions).

I suppose since you're only fixing generators, then that is literally
the only problem you are trying to fix, but it is more general than
that. I have encountered this sort of problem writing __next__ by hand
in Python -- that is, that bugs inside code I call result in silent
control flow changes rather than a visible exception.

-- Devin